Influence of age on pelvic inlet and outlet radiographic views

Background. Unstable fractures of the posterior pelvic ring represent a pressing concern in trauma surgery. Minimally invasive osteosynthesis techniques have gained widespread acceptance in contemporary practice. Accurate radiographic visualization is a critical component for the precise and successful placement of iliosacral and transsacral screws. Obtaining and accurately interpreting X-ray images can pose challenges in specific clinical situations, particularly those involving age-related skeletal changes.

The aim of the study is to assess the influence of the patient’s age on the measures of pelvic radiographic inlet and outlet views angles for performing a sacral fracture fixation using cannulated screws.

Methods. A retrospective analysis of CT data was conducted on 106 patients with posterior pelvic ring injuries requiring cannulated screw fixation. Preoperative CT scans were reconstructed into sagittal projections. We performed construction and measurement of the true inlet angle, super-inlet angle, pelvic outlet angle, sacral concavity angle, promontory angle, S1 and S2 outlet view angles. Statistical correlation between sacral tilt angle and the patient’s age was assessed.

Results. A two-step cluster analysis divided the patient cohort into two groups with significant differences in pelvic outlet angles and age (N1 = 64, N2 = 42). Statistically significant differences were found between the two clusters in all the studied parameters: median values of true pelvic inlet angles were 27.2° [23.2-32.2] and 18.2° [11.4-26.6] respectively (p<0.001); super-inlet angles were 42.5° [39.3-47.8] and 36.2° [28.7-42.8] respectively (p<0.001); promontory angles were 128.1° [123.3-133.2] and 122.1° [115.6-129.3] respectively (p = 0.003); pelvic outlet angles were 62.6° [58.4-69.6] and 50.3° [45.9-53.5] respectively (p<0.001); S1 outlet angles were 51.8° [48.9-56.5] and 46.8° [43.1-50.2] respectively (p<0.001); S2 outlet angles were 40.8° [37.3-44.6] and 35.7° [30.9-38.6] respectively (p<0.001); the mean of the sacral concavity angles was 174.8°±10.5 and 152.1°±38.2 respectively (p<0.001); and the main age was 41.6±18.7 and 69.2±16.1 years respectively (p<0.001). A statistically significant inverse correlation between age and pelvic tilt angle (ρ = 0.534; p<0.001) was found. A novel diagnostic method for identifying sacral dysmorphism using angle measurement within the S1 bone corridor is presented. The sacrum was considered dysmorphic if the angle was equal to or less than 5°.

Conclusions. As the patient’s age increases by one year, pelvic outlet angle decreases by 26°. If pelvic inlet angles are equal to or less than 14.45°, the difficulties in visualizing S1 and S2 outlet views during surgery are to be expected. The median of angles difference before and after anterior sacral tilt correction using a coccyx pad was 9.4° with interquartile range from 7.8° to 11°. Significant anatomical variations in posterior pelvic ring structure were observed among the study cohort. Preoperative CT sagittal reconstructions allow appropriate planning of intraoperative visualization considering expected intraoperative radiographic inlet and outlet views.